Sorter conveyors comprising a plurality of cross-belt units for supporting articles and transport these along a stationary track part forming a closed loop from one or more induction stations to a plurality of different discharge stations are well-known in the art.
A problem with respect to such sorter conveyors is that a drive unit must be provided for each cross-belt unit to move said belt for discharge of articles and, in case of induction of articles from the side of the sorter conveyor, also during induction of the articles. Commonly, each cross-belt unit is provided with a separate electric motor that is expensive to provide and maintain and which requires a transfer of power to the moving part of the sorter conveyor by means of e.g. inductive energy transfer or an electrical rail and collector shoes. Also, a control system must be provided on the moving part of the sorter conveyor as well as means for transferring control signals to said control system.
A known solution is to equip the sorter with stationary electric stator parts capable of producing a pulsating electrical field where a movement of the cross-belts may be required, and to equip each cross-belt unit with a drive part that is susceptible to said electrical field such that the cross-belts may be driven by means of the stationary electric stator part, thus making the provision of complete electric motors on the moving part of the sorter conveyor redundant.
It is known from FR 2 096 810 by Jeumont-Schneider to provide each cross-belt with a plurality of metallic strips parallel to the direction of movement of the sorter, thereby making the belt itself susceptible to the field from the stationary electric stator parts.
A solution allowing the use of standard cross-belts is disclosed in EP 0 425 021 by Van den Goor, in which a reaction roller being susceptible to the field for the stationary electric stator part is provided on each cross-belt unit, wherein the cross-belt is in contact with the reaction roller over part of the circumference of said roller to provide drive force from the reaction roller to the belt by friction. The cross-belt is guided along the part of the circumference of the reaction roller being opposite to the part facing the stationary electric stator part by means of two rollers biasing the cross-belt towards the reaction roller.
It is a problem with the latter discussed sorter conveyor that the cross-belt requires contact with as large a part of the circumference of the reaction roller as possible in order to provide the necessary friction force between the cross-belt and the reaction roller, and the stationary electric stator parts requires magnetic contact with as large a part of the circumference of the reaction roller as well in order to provide a satisfactory degree of efficiency of the system for driving the cross-belt. However, the cross-belt and the two biasing rollers limit the circumferential part of the reaction roller available to the stationary electric stator parts. Thus, both the cross-belt and the stationary electric stator parts requires access to as large a part of the circumference of the reaction roller as possible.
It is an object of the present invention to provide a cross-belt sorter conveyor with stationary electric stator parts for driving the cross-belts, in which the above-discussed problem of access to the circumference of the reaction roller for both the cross-belt and the stationary electric stator parts is relieved.
One solution would be to guide the cross-belt around the reaction roller between the reaction roller and the stationary electric stator parts but this results is an increased distance or gap between the reaction roller and the stationary electric stator parts, resulting in an increased magnetic reluctance and a lower efficiency of the drive system.
The solution provided with the present invention is to separate the function of the known reaction roller into a rotor being susceptible to the field of the stationary electric stator parts, a drive roller which over a part of its circumference is in driving contact with the cross-belt, and a transmission between the rotor and the drive roller for transmitting the drive force there between.
This solution provides other advantages as well. The two biasing rollers are made redundant and simpler bearing may be used for the rotor as compared to the reaction roller of the prior art because the bearing is relieved from the forces due to the internal stress of the cross-belt.
The separation of the function of the reaction roller into the rotor and the drive roller also permit a gearing between the two by means of the transmission, such that the circumferential speed of the rotor may be different from, and in particular higher than that of the drive roller. Thereby, a given rotor may yield more power as the power is proportional with the circumferential speed. Furthermore, a feed-back system for providing a measure of the movement of the cross-belt to the stationary control system of the sorter conveyor by means of measuring the rotation of the rotor may be given a better resolution due to the gearing. A yet further advantage occur in case the cross-belt is locking means of braking the rotor when the units are passing curved parts of the stationary track by and a gearing is made between the rotor and the drive cylinder, as a locking torque applied to the rotor will be multiplied by the gearing ratio when acting on the cross-belt.
The separation of functions also allows for a more flexible design of the cross-belt units and facilitates that the rotor may be situated at the level of the tracks on which the sorter moves or even lower in order to be in close contact with the stationary electric stator parts.
Other objects and advantages of the present invention will be apparent from the description of the invention.
The present invention relates in a second aspect to a sorter conveyor comprising tilt-tray units for supporting articles and transport these along a stationary track part forming a closed loop from one or more induction stations to a plurality of different discharge stations, in which the tilt of the trays are driven by means of electric motors which has turned out to be advantageous and is disclosed e.g. in WO 00/71446. It is however expensive to provide each tilt-tray unit with a separate electric motor and to maintain or replace motors due to malfunction of the active parts of the motor. The motors require a transfer of power to the moving part of the sorter conveyor by means of e.g. inductive energy transfer or an electrical rail and collector shoes. Also, a control system must be provided on the moving part of the sorter conveyor as well as means for transferring control signals to said control system. This type of sorter conveyors have been improved by the second aspect of the present invention by providing at least one stationary electric stator part along the stationary track part of the sorter conveyor, the stator parts being arranged to selectively produce a travelling magnetic field, and by arranging a rotor susceptible to said travelling magnetic field on each tilt-tray unit such that it may apply a driving force to tilt the tray when co-operating with the at least one stationary electric stator part. Thus, the requirement of one electric motor and the provision of electric power and control signals on the moving part of the sorter conveyor are made redundant.
The present invention relates in a third aspect to a sorter conveyor having arranged along the stationary track part at least one stationary electric stator part that may be activated selectively to produce a travelling magnetic field, and for each article-supporting unit comprises a rotor susceptible to said travelling magnetic field and arranged to apply a driving force to the discharge means when co-operating with the at least one stationary electric stator part, such as according to the two first aspects of the present invention as discussed above. The sorter conveyor requires drive means for driving the moving part along the stationary track part, which drive means may be stationary linear motors interacting with reaction means on the moving part, such as an aluminium plate covering a steel plate for a linear asynchronous motor drive or a set of permanent magnets for a linear synchronous motor drive. In both cases, it has been found that an advantage may be obtained by letting one or more stationary linear motor stator parts interact with the rotors to produce a driving force to drive the sorter along the stationary track part, thus letting the rotors take the place of the separate reaction means and making the sorter lighter and less expensive in construction.
The present invention relates in a fourth aspect to a simple rotor and to a method of manufacturing such rotor. A rotor for interacting with a stationary electric stator in an asynchronous manner may comprise an inner steel tube covered by an outer tube of a suitable material, such as copper or preferably aluminium, the inner surface of the aluminium tube being in contact with the outer surface of the steel tube. Such rotors are commonly manufactured by processing said two surfaces to a mutual interference fit, e.g. by turning the tubes, where after the tubes are assembled to a rotor. The tolerances have to be small, as the length of the aluminium tube does not allow for much pressing force before giving in to buckling. This manufacturing method is labour-intensive and the rotors are therefore relatively expensive. One object of the present invention is to provide less expensive rotors.
Such rotor may according to the present invention comprise one actual tube and the second of the inner or outer tubular members consist of a length of material being deformed into a tubular shape fastened to the first tubular member so as to preserve the tubular shape of the second tubular member as well as the contact between the two tubular members. Thereby, the rotor may be manufactured in a less expensive manner.